1. Field of Invention
The invention relates to a recharge apparatus and method for liquid developing electrostatic printing systems. In particular, the invention relates to recharge of a photoreceptor having at least one toner image formed on its surface for subsequent exposure and development of another toner image on the photoreceptor.
2. Description of Related Art
Electrostatographic printing is well known and commonly used for copying or printing documents on a paper substrate. Electrostatographic printing is performed by forming a substantially uniform charge on a photoconductive member and exposing the photoconductive member to a pattern of light. Exposing the photoconductive member to the pattern of light generates a corresponding electrostatic latent image on the photoconductive member. Toner particles are then deposited onto the photoconductive member so that the toner particles are selectively deposited in either charged or discharged areas on the photoconductive member. The developed toner image is then typically transferred to a substrate and fixed to the substrate by heat and/or pressure. The photoreceptor is then cleaned of any residual toner or electric charge in preparation for another charge/electrostatic latent image generating/development process.
Electrostatographic printing systems typically develop an electrostatic latent image using toner particles either in powder form or suspended in a liquid carrier. In liquid developing systems, the liquid developer typically has about two percent by weight toner material distributed in the liquid carrier. An electrostatic latent image is developed by applying the liquid developer to the photoconductive member, whereby the toner particles are selectively attracted to the surface of the photoconductive member in accordance with an electrostatic latent image. Typically, the toner image on the photoconductive member immediately after development contains about 12% by weight particulate toner.
Some liquid developing systems perform an image-on-image (IOI) process in which successive layers of toner are built up on a photoreceptor to create a process color image. Therefore, in an IOI process, after a first toner layer is formed on the photoreceptor, the photoreceptor typically must be recharged and exposed before a next toner layer can be deposited on the photoreceptor. One process for recharging a photoreceptor is a "split recharge" process, in which a first charging device overcharges the photoreceptor and a second charging device applies a charge of opposite polarity to the photoreceptor to reduce the level of charge on the photoreceptor. A split recharge system for a powder developing system is described in U.S. Pat. No. 5,600,430 to Folkins et al., which is incorporated herein by reference in its entirety. As described in U.S. Pat. No. 5,600,430, a first charging device, such as a corona charging device, overcharges the photoreceptor to a level higher than a desired voltage level for exposure. A second charging device applies a charge of opposite potential to the photoreceptor to reduce the charge level on the photoreceptor to a desired pre-exposure level.